Preparation method of hard carbon derived from ficus elastica pneumatophore and application in battery negative electrode

Abstract

This invention discloses a method for preparing hard carbon derived from the aerial roots of banyan trees, belonging to the field of new energy materials technology. The method includes the following steps: Step 1: Freshly cut banyan aerial roots are washed, dried, crushed, and sieved; Step 2: Choline chloride (ChCl) and lactic acid (LA) are mixed in a certain proportion to prepare DES; Step 3: The DES from Step 2 is mixed with the banyan aerial root powder from Step 1 and reacted, then subjected to delignification. The delignified black liquor is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake, which is then dried in an oven; Step 4: The filter cake from Step 3 is ground into powder and calcined at a medium-low temperature to obtain pre-carbonized banyan aerial root powder; Step 5: The pre-carbonized powder from Step 4 is calcined at a medium-high temperature, acid-washed, and dried to obtain banyan aerial root-derived hard carbon. This invention discloses a green, environmentally friendly, and high-performance method for preparing derived hard carbon, applicable to battery anode materials, realizing the high-value utilization of biomass waste.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a method for preparing a hard carbon sodium-ion battery anode material derived from the aerial roots of banyan trees. Background Technology

[0002] With the advancement of technology, market demand for energy storage devices such as batteries continues to rise. Currently, carbon materials, metal oxides, and alloys are all research subjects in the battery field, with carbon materials attracting widespread attention due to their abundant reserves and low cost. However, graphite, a common lithium-ion battery anode material, performs extremely poorly in sodium-ion batteries, exhibiting a theoretically low specific capacity of only 31%. Therefore, we urgently need to develop a new type of sodium-ion battery anode material that is sustainable and has excellent performance.

[0003] Hard carbon, used as a negative electrode material in sodium-ion batteries, is mainly prepared through the pyrolysis of biomass waste, biopolymers, and synthetic polymers. Hard carbon is typically prepared by high-temperature carbonization under an inert atmosphere; however, hard carbon obtained through direct ultra-high temperature carbonization suffers from poor rate performance and poor long-term cycle stability. Patent CN115028157B involves low-temperature pre-carbonization of corn cobs and soybean residue followed by high-temperature calcination; this process is simple, but its rate performance is only average. Patent CN117466284A uses asphalt to surface-modify the biomass carbon source, resulting in excellent performance, but the operation is relatively cumbersome. Therefore, a suitable biomass material is needed that achieves good performance through a simple process.

[0004] Banyan aerial roots, a type of landscaping waste with high cellulose content, possess excellent antibacterial and antifungal properties, moderate elongation, and good hygroscopic and rehydration capabilities. Their naturally porous structure is highly suitable for constructing carbon materials. However, research on using banyan aerial roots to derive hard carbon as an electrode material is still limited.

[0005] Therefore, developing a green and environmentally friendly method for preparing hard carbon using banyan aerial roots as raw material and improving the electrochemical performance of hard carbon has become an urgent problem to be solved in this field. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the technical problem to be solved by the present invention is to propose a method for preparing hard carbon derived from the aerial roots of banyan trees with green and environmentally friendly raw materials and excellent performance.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing hard carbon derived from the aerial roots of banyan trees, comprising the following steps:

[0009] Step 1: After washing and drying the freshly cut aerial roots of the banyan tree, crush and sieve them.

[0010] Step 2: Prepare DES by mixing choline chloride (ChCl) and lactic acid (LA) in a certain proportion;

[0011] Step 3: After mixing and reacting the DES from Step 2 with the banyan aerial root powder from Step 1, the mixture is deligated. The black liquor after deligation is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0012] Step 4: Grind the filter cake from Step 3 into powder and then... Low-temperature calcination yields pre-carbonized powder of banyan aerial roots;

[0013] Step 5: Place the pre-carbonized powder from Step 4 in... After calcination at medium and high temperatures, acid washing and drying are performed to obtain hard carbon derived from the aerial roots of banyan trees.

[0014] The preferred technical solution of the present invention is that, in step 1, aerial roots that have been preliminarily lignified in the lower part of the banyan tree trunk are selected, rinsed with deionized water and anhydrous ethanol to remove impurities, dried in an oven, and then pulverized to 80-100 mesh.

[0015] A preferred embodiment of the present invention is that, in step 2, ChCl and LA are added to a beaker in a molar ratio of 1:2 to 1:10, and mixed in an oil bath at 60°C to 80°C for 1 to 2 hours, and then cooled to room temperature for later use.

[0016] The preferred technical solution of the present invention is that, in step 3, the aerial root powder of banyan tree is weighed and mixed with DES in an oil bath at a mass ratio of 1:10 to 1:20 for 2 to 10 hours. During the reaction, a reflux condenser is used to prevent the DES solution from evaporating due to heat.

[0017] A preferred embodiment of the present invention is that, in step 4, the filter cake treated with DES is ground into powder and then placed in a tube furnace and introduced... At 3~5℃ The temperature was increased from room temperature to 400℃~600℃, held for 2 hours, and then increased at a rate of 3~5℃. The cooling rate is from 400℃~600℃ to room temperature.

[0018] A preferred embodiment of the present invention is that, in step 5, the pre-carbonized powder is placed in a tube furnace and air is introduced. At 3~5℃ The heating rate was increased from room temperature to 1000℃~1600℃, held for 2 hours, and then increased at 3~5℃. The cooling rate is from 1000℃~1600℃ to room temperature.

[0019] The preferred technical solution of the present invention is that, in step 5, hydrochloric acid is used for pickling, the concentration of which is 0.5~1M, and the cleaning is carried out at a speed of 500~600rpm. After cleaning for 4~6 hours, deionized water is used to clean until neutral, and the hard carbon derived from the aerial roots of the banyan tree is dried in an oven.

[0020] A type of hard carbon derived from the aerial roots of banyan trees, prepared according to a method.

[0021] Application of hard carbon derived from the aerial roots of banyan trees in the negative electrode of a battery.

[0022] A preferred embodiment of the present invention is that the method for preparing the battery negative electrode includes the following steps:

[0023] Step 1: According to the mass ratio, the hard carbon derived from banyan aerial roots: acetylene black: PVDF = 8:1:1, mix with 500±50 Add NMP to a 10 mL sample vial and stir at 1000-1200 rpm for 10-12 h;

[0024] Step 2: Coat the stirred mixture evenly onto the current collector and dry it under vacuum at 80°C for 12-14 hours to obtain the electrode sheet;

[0025] Step 3: Cut the dried electrode into circular electrode sheets with a diameter of 12mm, and use a sodium metal sheet as a reference electrode to provide a sodium source;

[0026] Step 4: Use An electrolyte with a ratio of 1:1:1 was used to test the rate performance and cycle performance of the electrode plates.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention uses the aerial roots of discarded banyan trees as raw materials to achieve high-value utilization of biomass waste and significantly reduce the raw material cost of hard carbon preparation; it uses a low eutectic solvent (DES) for lignin removal, which is more environmentally friendly and recyclable than traditional acid / alkali / organic solvents, and the washing process does not generate highly toxic waste liquid.

[0029] The hard carbon prepared by this invention has a composite structure of multi-level channels and fiber substrate layers, achieving precise synergy between structure and electrochemical performance. This not only facilitates electrolyte penetration but also provides sufficient ion storage sites, significantly improving the long-term stability of the battery.

[0030] When used as a battery negative electrode, this invention exhibits high specific capacity, good rate performance, and cycle stability, meeting the practical application requirements of energy storage devices. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the cross-section of the aerial roots of the banyan tree provided in a specific embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the cross-section of the aerial roots of a banyan tree provided in a specific embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram illustrating the performance of DES processing at different times according to a specific embodiment of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] A method for preparing hard carbon derived from the aerial roots of banyan trees includes the following steps:

[0037] Step 1: Select the aerial roots that have been preliminarily lignified from the middle and lower part of the banyan tree branches, rinse them three times each with deionized water and anhydrous ethanol, dry them in an oven, and then crush them through a 100-mesh sieve.

[0038] Step 2: Add ChCl and LA in a molar ratio of 1:10 into a beaker, mix in an oil bath at 80°C for 1 hour, and then cool to room temperature to obtain DES;

[0039] Step 3: React DES and banyan aerial root powder in an oil bath at 120°C for 2 hours at a mass ratio of 1:10. The reaction process is carried out by a reflux condenser to prevent the DES solution from evaporating due to heat. The black liquor after the reaction is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0040] Step 4: Grind the dried filter cake into powder, add it to a crucible, transfer it to a tube furnace, and then introduce air. At 3℃ The temperature was increased from room temperature to 500°C, held for 2 hours, and then increased at a rate of 3°C. The temperature was reduced from 500℃ to room temperature to obtain pre-carbonized powder of banyan aerial roots;

[0041] Step 5: Place the pre-carbonized powder of banyan aerial roots in... China and Israel 5℃ The heating rate was increased from room temperature to 1400℃, held at that temperature for 2 hours, and then reduced at 5℃. The temperature was cooled from 1400℃ to room temperature to obtain hard carbon derived from the aerial roots of banyan trees. The hard carbon material was washed with 1M HCl solution for 6 hours, then rinsed with deionized water until neutral, and finally dried in an oven at 80℃.

[0042] Comparative Example 1

[0043] The preparation steps are the same as in Example 1, except that the molar ratio of ChCl to LA is 1:2.

[0044] Comparative Example 2

[0045] The preparation steps are the same as in Example 1, except that the molar ratio of ChCl to LA is 1:5.

[0046] Example 2

[0047] A method for preparing hard carbon derived from the aerial roots of banyan trees includes the following steps:

[0048] Step 1: Select the aerial roots that have been preliminarily lignified from the middle and lower part of the banyan tree branches, rinse them three times each with deionized water and anhydrous ethanol, dry them in an oven, and then crush them through a 100-mesh sieve.

[0049] Step 2: Add ChCl and LA in a molar ratio of 1:10 into a beaker, mix in an oil bath at 80°C for 1 hour, and then cool to room temperature to obtain DES;

[0050] Step 3: React DES and banyan aerial root powder in an oil bath at 120°C for 4 hours at a mass ratio of 1:10. The reaction process is carried out by a reflux condenser to prevent the DES solution from evaporating due to heat. The black liquor after the reaction is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0051] Step 4: Grind the dried filter cake into powder, add it to a crucible, transfer it to a tube furnace, and then introduce air. At 3℃ The temperature was increased from room temperature to 500°C, held for 2 hours, and then increased at a rate of 3°C. The temperature was reduced from 500℃ to room temperature to obtain pre-carbonized powder of banyan aerial roots;

[0052] Step 5: Place the pre-carbonized powder of banyan aerial roots in... China and Israel 5℃ The heating rate was increased from room temperature to 1400℃, held at that temperature for 2 hours, and then reduced at 5℃. The temperature was cooled from 1400℃ to room temperature to obtain hard carbon derived from the aerial roots of banyan trees. The hard carbon material was washed with 1M HCl solution for 6 hours, then rinsed with deionized water until neutral, and finally dried in an oven at 80℃.

[0053] Comparative Example 3

[0054] The preparation steps are the same as in Example 2, except that the molar ratio of ChCl to LA is 1:2.

[0055] Comparative Example 4

[0056] The preparation steps are the same as in Example 2, except that the molar ratio of ChCl to LA is 1:5.

[0057] Example 3

[0058] A method for preparing hard carbon derived from the aerial roots of banyan trees includes the following steps:

[0059] Step 1: Select the aerial roots that have been preliminarily lignified from the middle and lower part of the banyan tree branches, rinse them three times each with deionized water and anhydrous ethanol, dry them in an oven, and then crush them through a 100-mesh sieve.

[0060] Step 2: Add ChCl and LA in a molar ratio of 1:10 into a beaker, mix in an oil bath at 80°C for 1 hour, and then cool to room temperature to obtain DES;

[0061] Step 3: React DES and banyan aerial root powder in an oil bath at 120°C for 6 hours at a mass ratio of 1:10. During the reaction, a reflux condenser is used to prevent the DES solution from evaporating due to heat. The black liquor after the reaction is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0062] Step 4: Grind the dried filter cake into powder, add it to a crucible, transfer it to a tube furnace, and then introduce air. At 3℃ The temperature was increased from room temperature to 500°C, held for 2 hours, and then increased at a rate of 3°C. The temperature was reduced from 500℃ to room temperature to obtain pre-carbonized powder of banyan aerial roots;

[0063] Step 5: Place the pre-carbonized powder of banyan aerial roots in... China and Israel 5℃ The heating rate was increased from room temperature to 1400℃, held at that temperature for 2 hours, and then reduced at 5℃. The temperature was cooled from 1400℃ to room temperature to obtain hard carbon derived from the aerial roots of banyan trees. The hard carbon material was washed with 1M HCl solution for 6 hours, then rinsed with deionized water until neutral, and finally dried in an oven at 80℃.

[0064] Comparative Example 5

[0065] The preparation steps are the same as in Example 3, except that the molar ratio of ChCl to LA is 1:2.

[0066] Comparative Example 6

[0067] The preparation steps are the same as in Example 3, except that the molar ratio of ChCl to LA is 1:5.

[0068] Example 4

[0069] A method for preparing hard carbon derived from the aerial roots of banyan trees includes the following steps:

[0070] Step 1: Select the aerial roots that have been preliminarily lignified from the middle and lower part of the banyan tree branches, rinse them three times each with deionized water and anhydrous ethanol, dry them in an oven, and then crush them through a 100-mesh sieve.

[0071] Step 2: Add ChCl and LA in a molar ratio of 1:10 into a beaker, mix in an oil bath at 80°C for 1 hour, and then cool to room temperature to obtain DES;

[0072] Step 3: React DES and banyan aerial root powder in an oil bath at 120°C for 8 hours at a mass ratio of 1:10. The reaction process is carried out by a reflux condenser to prevent the DES solution from evaporating due to heat. The black liquor after the reaction is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0073] Step 4: Grind the dried filter cake into powder, add it to a crucible, transfer it to a tube furnace, and then introduce air. At 3℃ The temperature was increased from room temperature to 500°C, held for 2 hours, and then increased at a rate of 3°C. The temperature was reduced from 500℃ to room temperature to obtain pre-carbonized powder of banyan aerial roots;

[0074] Step 5: Place the pre-carbonized powder of banyan aerial roots in... China and Israel 5℃ The heating rate was increased from room temperature to 1400℃, held at that temperature for 2 hours, and then reduced at 5℃. The temperature was cooled from 1400℃ to room temperature to obtain hard carbon derived from the aerial roots of banyan trees. The hard carbon material was washed with 1M HCl solution for 6 hours, then rinsed with deionized water until neutral, and finally dried in an oven at 80℃.

[0075] Comparative Example 7

[0076] The preparation steps are the same as in Example 4, except that the molar ratio of ChCl to LA is 1:2.

[0077] Comparative Example 8

[0078] The preparation steps are the same as in Example 4, except that the molar ratio of ChCl to LA is 1:5.

[0079] Example 5

[0080] A method for preparing hard carbon derived from the aerial roots of banyan trees includes the following steps:

[0081] Step 1: Select the aerial roots that have been preliminarily lignified from the middle and lower part of the banyan tree branches, rinse them three times each with deionized water and anhydrous ethanol, dry them in an oven, and then crush them through a 100-mesh sieve.

[0082] Step 2: Add ChCl and LA in a molar ratio of 1:10 into a beaker, mix in an oil bath at 80°C for 1 hour, and then cool to room temperature to obtain DES;

[0083] Step 3: React DES and banyan aerial root powder in an oil bath at 120°C for 10 hours at a mass ratio of 1:10. The reaction process is carried out through a reflux condenser to prevent the DES solution from evaporating due to heat. The black liquor after the reaction is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven.

[0084] Step 4: Grind the dried filter cake into powder, add it to a crucible, transfer it to a tube furnace, and then introduce air. At 3℃ The temperature was increased from room temperature to 500℃, held for 8 hours, and then increased at a rate of 3℃. The temperature was reduced from 500℃ to room temperature to obtain pre-carbonized powder of banyan aerial roots;

[0085] Step 5: Place the pre-carbonized powder of banyan aerial roots in... China and Israel 5℃ The heating rate was increased from room temperature to 1400℃, held at that temperature for 2 hours, and then reduced at 5℃. The temperature was cooled from 1400℃ to room temperature to obtain hard carbon derived from the aerial roots of banyan trees. The hard carbon material was washed with 1M HCl solution for 6 hours, then rinsed with deionized water until neutral, and finally dried in an oven at 80℃.

[0086] Comparative Example 9

[0087] The preparation steps are the same as in Example 5, except that the molar ratio of ChCl to LA is 1:2.

[0088] Comparative Example 10

[0089] The preparation steps are the same as in Example 5, except that the molar ratio of ChCl to LA is 1:5.

[0090] Table 1

[0091] Combined with appendix Figure 1-3 The performance comparison results with Table 1 show that:

[0092] 1. A molar ratio of 1:10 for ChCl to LA is more optimal.

[0093] In the examples, the molar ratio of ChCl to LA was 1:10. Compared with the comparative examples with molar ratios of 1:2 and 1:5 under the same reaction conditions, the hard carbon with a 1:10 ratio showed more balanced performance.

[0094] In Example 1, the initial coulombic efficiency of the sample was 72.16%, which was better than 69.12% in Comparative Example 1 and 65.44% in Comparative Example 2; the 200-cycle capacity retention rate of the sample in Example 1 was 78.66%, which was better than 75.44% in Comparative Example 1 and 74.56% in Comparative Example 2; the 200-cycle capacity retention rate of the sample in Example 2 was 80.11%, which was much higher than 74.55% in Comparative Example 1 and 75.66% in Comparative Example 4; the initial coulombic efficiency of the sample in Example 3 was 71.03%, which was close to 70.14% in Comparative Example 5, but better than 68.55% in Comparative Example 6.

[0095] Therefore, using a DES formulation of ChCl:LA=1:10 can form a highly efficient biomass component activation system. This system can selectively remove impurities such as lignin and hemicellulose from the aerial roots of banyan trees while retaining the carbon-rich cellulose matrix. It can also uniformly introduce oxygen-containing functional groups onto the surface of the carbon precursor, providing a precise "template" for the pore structure and carbon layer regularity of subsequent carbonization. Compared to the molar ratios of ChCl to LA of 1:2 and 1:5, the 1:10 ratio results in a more uniform surface for hard carbon, balancing capacity, first-time efficiency, and cycle stability.

[0096] 2. The optimal performance of DES with banyan aerial root powder is achieved when the reaction time is 6 hours.

[0097] The examples and comparative examples demonstrate the effect of reaction time on the generation of hard carbon from the aerial roots of Ficus microcarpa by adjusting the reaction time to 2h, 4h, 6h, 8h, and 10h.

[0098] In Example 3, when the reaction time between DES and banyan aerial root powder was 6 hours, the reversible specific capacity was 376.97. Among all samples, the reversible specific capacity was the highest, and the capacity retention rate after 200 cycles was 80.65%, which was also at the optimal level. In Examples 1 and 2, the reaction time of DES with the aerial root powder of Banyan Tree was 2h and 4h, respectively, which was shorter than that of Example 3. The reversible specific capacity and the capacity retention rate after 200 cycles were also slightly weaker than those of Example 3. In Examples 4 and 5, the reaction time of DES with the aerial root powder of Banyan Tree was 8h and 10h, respectively, which was longer than that of Example 3. The reversible specific capacity and the capacity retention rate after 200 cycles were significantly lower than those of Example 3. This indicates that a reaction time of 6h allows DES and the aerial root powder of Banyan Tree to fully interact and form a pore structure / interlayer spacing that is more conducive to ion storage. Insufficient reaction time results in insufficient modification, while excessive reaction time will damage the material structure and lead to a decrease in energy storage capacity. The hard carbon material prepared by reacting for 6h has a more reasonable internal pore and conductive network and a faster ion transport rate, thus exhibiting better rate performance. The aerial root-derived hard carbon anode material of Banyan Tree after 6h of DES treatment has excellent stability during long-term cycling.

[0099] This invention uses waste banyan aerial roots as raw materials to replace traditional fossil-based carbon sources. Combined with DES green solvent, the carbon emissions and costs of the preparation process are reduced by about 15% to 20%. At the same time, compared with commercial hard carbon, the materials prepared by this method achieve a balance of performance in terms of high capacity, long cycle life, and high rate capability, and have greater potential for industrial application.

[0100] This invention has been described through preferred embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. This invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims are also within the protection scope of this invention.

Claims

1. A method for preparing hard carbon derived from the aerial roots of banyan trees, characterized in that: Includes the following steps: Step 1: After washing and drying the freshly cut aerial roots of the banyan tree, crush and sieve them. Step 2: Prepare DES by mixing choline chloride (ChCl) and lactic acid (LA) in a certain proportion; Step 3: After mixing and reacting the DES obtained in Step 2 with the banyan aerial root powder in Step 1, the mixture is deligated. The black liquor after deligation is washed with anhydrous ethanol and deionized water and filtered to obtain a filter cake. The filter cake is then dried in an oven. Step 4: Grind the filter cake from Step 3 into powder and then... Low-temperature calcination yields pre-carbonized powder of banyan aerial roots; Step 5: Place the pre-carbonized powder from Step 4 in... After calcination at medium and high temperatures, acid washing and drying are performed to obtain hard carbon derived from the aerial roots of banyan trees.

2. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 1, aerial roots that have been preliminarily lignified in the lower part of the banyan tree trunk are selected, rinsed with deionized water and anhydrous ethanol to remove impurities, dried in an oven, and then pulverized to 80-100 mesh.

3. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 2, ChCl and LA are added to a beaker at a molar ratio of 1:2 to 1:10, and then mixed in an oil bath at 60°C to 80°C for 1 to 2 hours before cooling to room temperature for later use.

4. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 3, the aerial root powder of banyan tree is weighed and mixed with DES at a mass ratio of 1:10 to 1:20 in an oil bath at 90℃ to 150℃ for 2 to 10 hours. During the reaction, a reflux condenser is used to prevent the DES solution from evaporating due to heat.

5. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 4, the filter cake treated with DES is ground into powder and then placed in a tube furnace and introduced. At 3~5℃ The temperature was increased from room temperature to 400℃~600℃, held for 2 hours, and then increased at a rate of 3~5℃. The cooling rate is from 400℃~600℃ to room temperature.

6. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 5, the pre-carbonized powder is placed in a tube furnace and air is introduced. At 3~5℃ The heating rate was increased from room temperature to 1000℃~1600℃, held for 2 hours, and then increased at 3~5℃. The cooling rate is from 1000℃~1600℃ to room temperature.

7. The method for preparing hard carbon derived from the aerial roots of banyan trees according to claim 1, characterized in that: In step 5, hydrochloric acid is used for pickling at a concentration of 0.5-1M and a rotation speed of 500-600 rpm. After 4-6 hours of pickling, deionized water is used to rinse until neutral. The hard carbon derived from the aerial roots of the banyan tree is then dried in an oven.

8. A type of hard carbon derived from the aerial roots of banyan trees prepared by the method described in any one of claims 1-7.

9. The application of hard carbon derived from the aerial roots of banyan trees as described in claim 8 in the negative electrode of a battery.

10. The application of the hard carbon derived from the aerial roots of the banyan tree according to claim 9 in the negative electrode of a battery, characterized in that: The method for preparing the negative electrode of the battery includes the following steps: Step 1: According to the mass ratio, the hard carbon derived from banyan aerial roots: acetylene black: PVDF = 8:1:1, mix with 500±50 Add NMP to a 10 mL sample vial and stir at 1000-1200 rpm for 10-12 h; Step 2: Coat the stirred mixture evenly onto the current collector and dry it under vacuum at 80°C for 12-14 hours to obtain the electrode sheet; Step 3: Cut the dried electrode into circular electrode sheets with a diameter of 12mm, and use a sodium metal sheet as a reference electrode to provide a sodium source; Step 4: Use An electrolyte with a ratio of 1:1:1 was used to test the rate performance and cycle performance of the electrode plates.

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